This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The purpose of this study is to determine the safety and efficacy of an exercise rehabilitation program in patients with pulmonary arterial hypertension (PAH). This study will recruit 16 patients for participation in the proposed trial. All patients will have a blood test at baseline and undergo 6-minute walk testing and CPET (increasing workload, to maximum) at baseline in order to examine how their pulmonary hypertension affects their ability to deliver oxygen to their muscles in response to exercise. All patients will also complete a questionnaire to rate their quality of life (SF-36 questionnaire), and will have a second CPET (constant workload, to fatigue). Patients will undergo formal exercise training for 6 weeks under the supervision of a physician and physical therapist in J-4, a facility that has a well-established protocol for intensive, short duration exercise training. AFter 6 weeks, the CPEts, questionnaire, and blood tests will be repeated.